The ability of crystalline alkali metal aluminosilicate (zeolite) to sequester calcium ions from aqueous solution has led to its becoming a well-known replacement for phosphates as a detergency builder. Particulate detergent compositions containing zeolite are widely disclosed in the art, for example, in GB 1 473 201 (Henkel), and are sold commercially in many parts of Europe, Japan and the United States of America.
Although many crystal forms of zeolite are known, the preferred zeolite for detergents use has always been zeolite A: other zeolites such as X or P(B) have not found favour because their calcium ion uptake is either inadequate or too slow. Zeolite A has the advantage of being a "maximum aluminium" structure containing the maximum possible proportion of aluminium to silicon--or the theoretical minimum Si:Al ratio of 1.0--so that its capacity for taking up calcium ions from aqueous solution is intrinsically greater than those of zeolite X and P which generally contain a lower proportion of aluminium (or a higher Si:Al ratio).
EP 384 070A (Unilever) describes and claims a novel zeolite P (maximum aluminium zeolite P, or zeolite MAP) having an especially low silicon to aluminium ratio, not greater than 1.33 and preferably not greater than 1.15. This material is demonstrated to be a more efficient detergency builder than conventional zeolite 4A.
Sodium percarbonate is a well-known bleaching ingredient in detergent compositions and is widely disclosed in the literature, although in recent years its use in commercial products has been abandoned in favour of sodium perborate. Sodium percarbonate is less stable than sodium perborate in the presence of moisture, and its stabilisation in detergent powders has long been recognised as a problem to which various solutions have been suggested; for example, GB 1 515 299 (Unilever) discloses the stabilisation of sodium percarbonate in a detergent composition by admixture with a perfume diluent, for example, dibutyl phthalate.
The problem becomes especially acute if sodium percarbonate is to be included in a detergent powder with a high free moisture content, when it tends to become deactivated on storage. This situation applies in particular to powders containing zeolites, because those materials contain a large amount of relatively mobile water.
Detergent compositions containing alkali metal aluminosilicate (type 4A zeolite) and sodium percarbonate are disclosed in DE 2 656 009A (Colgate), in Examples 1 and 2, but storage stability is not discussed. According to GB 2 013 259A (Kao), the problem of sodium percarbonate stability in the presence of hydrated crystalline zeolites is solved by the use of an amorphous or partially crystalline aluminosilicate (0-75% crystallinity) or by the use of a partially calcium- or magnesium-exchanged material.
It has now unexpectedly been found that replacement of zeolite A by maximum aluminium zeolite P (zeolite MAP) which is the subject of EP 384 070A (Unilever) has a significantly beneficial effect on sodium percarbonate stability. This is surprising because the water content of zeolite MAP is not significantly lower than that of zeolite A.